In the field of semiconductor device fabrication, there are various methods for separating a wafer into die, including scribe and break techniques. In scribe and break techniques, the die is separated by breaking the wafer along scribe lines, which can be cut in the wafer in a number of ways. For example, wafers having semiconductor substrates can be mechanically scribed, such as with a diamond. In wafers having sapphire substrates, laser scribing has been disclosed, as, for example, in U.S. patent application No. 09/178,287, entitled, “Semiconductor Device Separation Using a Patterned Laser Projection,” which is incorporated herein by reference. The device separation method disclosed therein uses laser ablation to form scribe lines in the wafer.
Because scribing removes material from the wafer, some scribing techniques can result in the buildup of waste material on the wafer. In laser ablation scribing, for example, waste substrate material, also referred to as slag, tends to form as residue on the wafer. The slag forms on the sidewall and around the die perimeter, building from the bottom of the cut to the top. That is, there tends to be more slag near the top of the cut than the bottom. Slag around the die perimeter can degrade the reliability of the device and inhibit wire bonding. In optical devices, such as LED's and lasers, sidewall buildup can decrease the power output of the device, as the slag can absorb some of the optical output power of the device.
It has been suggested that a protective coating of a photoresist material can be used to protect the topside of the die from waste material. The material is applied and then cured to form the protective coating. The coating, of course, must be removed at some point in the separation process, such as by using a solvent. Known uses of photoresist protective coating techniques tend to decrease process times as additional activities or steps must be carried out in the separation process. In device fabrication, processes that deliver high yields in short times are desirable, as even relatively minor increases in efficiency can lead to significant increases in device throughput.